This application is based on Japanese Patent Application No. 2001-374038 filed on Dec. 7, 2001, the disclosure of which is incorporated herein by reference.
The present invention relates to a rotary electric machine in which coil ends of upper layer coils mounted on an armature core constructs a commutator.
In a rotary electric machine disclosed in JP-A-8-168225 (U.S. Pat. Nos. 5,739,617 and 6,018,209), coil ends of upper layer coils installed in an armature core are used as a commutator. Collars are fixed on an armature rotation shaft to restrict the coil ends from expanding or separating from axial ends of the armature core due to a centrifugal force during the armature rotation.
Each of the collars has a cylindrical portion fitted around the rotation shaft, a flange integrated with the cylindrical portion, and a ring-shaped pressing portion bent from the outer circumferential edge of the flange toward the coil ends of the upper layer coils. The pressing portion presses the coil ends through an insulator.
In this rotary electric machine, when the upper layer coils and lower layer coils are supplied with electricity, the coils generate heat and thermally expand. Because the upper layer coils and the lower layer coils are made of low electric resistance material such as copper and the armature core and the rotation shaft are, for example, made of iron, the coils have a coefficient of thermal expansion greater than that of the armature core and rotation shaft. Therefore, the thermal expansion of the coils causes a force pushing the collar.
The force is exerted to the collar in a direction removing the collar from the rotation shaft, that is, a direction separating from the armature core. When the collar is moved from the predetermined position by the force, the pressing portion cannot press the coil ends equally. As a result, the coil ends are likely to separate from the armature core. This causes gaps on the commutator surfaces, resulting in poor commutation. Further, power output is lessened. Also, wear of brushes increases, thereby reducing lives of the brushes.
When the collar moves from the predetermined position and is unable to press the coil ends, the coil ends vibrate. With this, insulator interposed between the pressing portion and the coil ends are damaged. As a result, the coils are likely to short one another through the collar.
The present invention is made in view of the above disadvantages, and it is an object of the present invention to provide a rotary electric machine in which a collar is restricted from moving due to thermal expansion of coil ends.
It is another object of the present invention to provide a rotary electric machine in which a collar presses against coil ends that construct a commutator even when the coil ends expand or contract due to thermal deformation of coils.
According to a rotary electric machine of the present invention, a plurality of unit coils is mounted on an armature core supported by a rotation shaft and constructs an armature coil. Each unit coil includes a lower layer coil and an upper layer coil arranged in double layers. Coil ends of the lower layer coils and the upper layer coils are located parallel to an axial end surface of the armature core. A pressing member for pressing the coil ends toward the armature core includes a cylindrical portion fitted on the rotation shaft, a flange radially extending from the cylindrical portion and a pressing portion in contact with an insulator interposed between the coil ends and the pressing portion.
Even when the coil ends expand and contract in the axial direction due to thermal deformation of the coils, the pressing portion presses against the coil ends toward the armature core through the insulator by resiliency of the flange and the cylindrical portion is maintained at a predetermined position on the rotation shaft.
Accordingly, since expansion of the coil ends is restricted by the pressing member, axial end surfaces of the coil ends of the upper layer coils on which brushes slide-contact can be maintained smooth. Therefore, poor contact or poor commutation of the brushes is decreased. Further, wear of brushes is suppressed. In addition, since the pressing portion presses against the coil ends through the insulator, vibrations of the coil ends are restricted. Therefore, damage to the insulator is decreased.
Alternatively, a pressing member for pressing the coil ends toward the armature core includes a cylindrical portion fixed on the rotation shaft. The rotation shaft includes a restricting member for restricting the cylindrical portion from moving in a direction separating from the armature core. Accordingly, even when the coil ends expand, the cylindrical portion is restricted from moving in the direction separating from the armature core and the pressing portion presses against the coil ends.